Physics Lights and Optics Online Mcqs Test

Maan AliLast Updated: October 13, 2025

Important Lights and Optics Question and Answer

Total Questions:	88
Time Allowed:	40 Minutes
Total Marks:	88
How to Attempt Test:	Please choose the right Option in MCQ-type question.
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Physics Lights and Optics Practice Test Online With Explanation

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Page 1 of 4

Physics

1. Fraunhoffer’s lines commonly visible in the sun’s spectrum are examples of

Band emission spectrum

Line absorption spectrum

Line emission spectrum

Band absorption spectrum

2. Curtain less windows are made by making use of __________ of light.

Polarization

Transmission

Absorption

Diffraction

3. The cause of mirage observed in desert is

Scattering

Reflection

Refraction

Total internal reflection

4. Coherent monochromatic light illuminates two narrow parallel slits and the interference pattern that results is observed on a screen some distance beyond the slits. Which modification increases the separation between the dark lines of the interference pattern?

Using monochromatic light of longer wavelength

Decreasing the distance between the screen and the slits

Using monochromatic light of higher frequency

Increasing the distance between the slits

5. In an interference pattern

Dark fringes are wider than bright fringe

Bright fringes are wider than dark fringes

Central fringes are brighter than the outer fringes

Both dark and bright fringes are of equal width

6. Ray optics is valid, when characteristic dimensions are

Of the order of one millimeter

Much larger than the wavelength of light

Much smaller than the wavelength of length

Of the same order as the wavelength of light

7. In Young double slit experiment, if white light is used

Impossible to predict

Colored fringes will be seen

Alternate dark and bright fringes will be seen

No interference fringes will be seen

8. A spectrum which contains all wavelengths without any break is called

Line spectrum

Continuous emission spectrum

Emission spectrum

All of these

9. In the Michelson Interferometer, if m number fringes pass through a reference point when the mirror is moved a distance d, then the wavelength of the light can be found by the formula:

λ = 2π dm

2λ = dm

λ = 2d/m

λ = dm

10. A spherical wave front is that which has

A point source

None of these

A extended source

A source

11. If the path difference must be half-integral number wavelength

d sin θ = (m + 1/2)λ

d sin θ = (m + 1)λ

d in θ = (m + ½ )1/λ

d sin θ = (m + 1/2)π/λ

12. If a source of light is moving away from stationary observer, then frequency of light wave appears to change because of

Interference

Doppler’s effect

None of these

Diffraction

13. A prism splits a beam of white light into its seven constituent colors. This is so because

Velocity of different colors is different

Energy of different colors is different

Amplitude of different colors is different

Phase of different colors is different

14. The locus of all points in a medium having the same phase of vibration is called

Crest

Wavelength

Wave front

Trough

15. When the light is incident on polarizing angle which of the following is completely polarized?

Neither reflected nor refracted light

Refracted light

Both reflected and refracted light

Reflected light

16. The blue colour of the sky is due to

Reflection

Scattering

Polarization

Diffraction

17. For constructive interference the path difference is

m²λ

½ mλ

Mλ

(m – 1)λ

18. In Young’s experiment, a dark fringe is observed when:

m Sin θ = (d + 1/2)λ

2π Sin θ = (m + 1/2)λ

½ d Sin θ = mλ

d Sin θ = (m + 1/2)λ

19. Wave front is the locus of all points in vibration are in the same

Frequency

Phase

Wavelength

All of these

20. Huygen’s wave fronts which sends out secondary wavelets with a speed equal to

Speed of propagation less than the wave

Speed of propagation of the wave

Speed of propagation greater than wave

B and C

21. Diffraction effect is

Less for a sharp edge

More for a round edge

More for a sharp edge

Less for a round edge

22. Wavelength of light of frequency 100 Hz is

4 x 10⁶ m

2 x 10⁶ m

3 x 10⁶ m

5 x 10⁶ m

23. An oil surface floating on water surface exhibits beautiful colour patter, which is due to

Reflection of light

Diffraction of light

Interference of light

None of these

24. Why laser rays are used to measure long distance?

Laser rays are most coherent waves

Laser rays are not absorbed

Laser rays propagate in a straight line

Laser rays are high velocity waves

25. Appearance of colour in thin films is due to

Polarization

Dispersion

Diffraction

Interference

Page 2 of 4

26. Due to Plano convex lens and the plane glass plate the thickness of air film changes from the center to outward

None of these

Increasing gradually

It is constant at the center

Decreasing gradually

27. Who devise the experimental arrangement is 1801 for studying interference effects of light?

Huygen

Young

None of these

Newton

28. For the sustained interference of light, the necessary condition is that the two sources should

Have constant phase difference

Be narrow

Of same amplitude

Be close to each other

29. The setting of Newton’s rings is

A Plano convex lens (long focal length) and the plane of glass plate

A Plano convex lens and simple glass sheet

None of these

A Plano convex lens and the plane glass plate

30. Light is a type of energy which produces sensation of

Sound

None of these

Feeling

Vision

31. In the phenomenon of interference, the bright ad dark fringes are of

None of these

Dark fringes are thicker than bright

Equal width

Different width

32. A diffraction grating has 500 lines per mm. Its slit spacing or grating element will be equal to

5 x 10¯³ mm

2 x 10¯³ mm

500 mm

2 x 10¯⁵ mm

33. Which one of the following phenomena is not explained by Huygen’s construction of wave front?

Refraction

Diffraction

Reflection

Origin of spectra

34. The fringe spacing in case of blue light

Decrease

None of these

Increases

Remains the same

35. A ____________ lens is used to form Newton’s rings.

Double-convex

Convexo-concave

Plano-concave

Plano-convex

36. Interference was observed in interference chamber, when air was present, now the chamber is evacuated and if the same light is used, a careful observer will see

No interference

Interference in which breadth of the fringe will be slightly increase

Interference with dark bands

Interference with bright bands

37. Two sources of light are coherent if they emit rays of

Same amplitude and wavelength

Same wavelength

Same amplitude of vibration

Same wave length with constant phase difference

38. Which one of the following cannot be polarized?

Sound waves

Ultraviolet rays

Radio waves

X-rays

39. The light produced by a laser is all the following except

Monochromatic

In the form of a narrow beam

Incoherent

Electromagnetic

40. In Newton’s rings the point of contact of the lend and the glass plate, the air film is

Maximum

Minimum

Zero

None of these

41. The relation of constructive interference in X-ray diffraction is called

Bragg’s law

Compton effect

Huygen’s formula

Laue’s pattern

42. Huygen’s wave theory of light cannot explain

Diffraction

Polarization

Photoelectric effect

Interference

43. Which of the following frequency ranges includes most of the electromagnetic waves emitted by the ultra – violet tubes used in a sun bed?

5 x 10⁵ to 5 x 10¹¹ Hz

5 x 10¹¹ to 5 x 10¹⁴ Hz

5 x 10⁵ to 5 x 10⁵ Hz

5 x 10¹⁴ to 5 x 10¹⁷ Hz

44. Every point of a wave front may be considered as a

Source of secondary wave front

Source of wave front

Source

None of these

45. The contrast in the fringes in any interference pattern depends on

Fringe width

Intensity ratio of the sources

Wavelength

Distance between the slits

46. Central spot of New tons rings

Bright

Dart for large wavelength

Bright for large wavelength

Dark

47. When crest of one wave falls over the trough of the other wave this phenomenon is known as

Destructive interference

Constructive interference

Diffraction

Polarization

48. Longitudinal waves do not exhibit

Diffraction

Refraction

Polarization

Reflection

49. If a wave can be polarized, it must be

A transverse waves

An electromagnetic wave

A longitudinal wave

A sound wave

50. The principle of Michelson’s interferometers is

Dispersion

Interference

Reflection

Refraction

Page 3 of 4

51. According to the electromagnetic theory, the speed of light is approximately:

3 x 10⁸ ms¯¹

3.1 x 10⁸ ms¯¹

3 x 10¯¹⁰ ms¯¹

3 x 10⁵ ms¯¹

52. The light produced by a laser is all the following except

Monochromatic

Electromagnetic

In the form of a narrow beam

Incoherent

53. Huygen’s wave theory of light cannot explain

Interference

Photoelectric effect

Diffraction

Polarization

54. If the dark fringe is to be observed then we have relation

Y = (m + 1/2) λd/L

Y = (m + ½) dL/λ

Y = (m + 1) λL/d

Y = (m + 1/2) λL/d

55. To demonstrate the phenomenon of interference we require two sources that emit radiation

Of nearly the same frequency

Different wavelength

Of the same frequency and having definite phase relationship

Of same frequency

56. Crystals of a material can behave as

Convex lens

Concave

Interferometer

Diffraction grating

57. The condition for constructive interference of two coherent beams is that the path difference should be

Odd integral multiple of λ/2

Even integral multiple of λ

Integral multiple of λ/2

Integral multiple of λ

58. Ultra – violet rays differ from X-rays in that ultra – violet rays

Do not affect a photographic plate

Cannot be polarized

Cannot be diffracted

Have a lower frequency

59. Which of the following has least wavelength?

Cosmic-rays

X-rays

Ultra-violet rays

γ-rays

60. Light on passing through a Polaroid is

Un-polarized

Elliptically polarized

Circularly polarized

Plane polarized

61. A point source of light placed in a homogeneous medium gives rise to

An elliptical wave front

A spherical wave front

A plane wave front

A cylindrical wave front

62. According to Huygen, every point on a wave front may be regarded as a __________ of secondary wavelets.

Base

Producer

Origin

Source

63. On a rainy day, if there is an oil drop on tar road, colored rings are seen around this drop. This is because of

Total internal reflection of light

Polarization

Interference pattern produced due to thin oil film

Diffraction pattern

64. Which one of the following phenomena is not explained by Hygen’s construction of wave front?

Diffraction

Reflection

Origin of spectra

Refraction

65. One condition for interference is that the two sources should be coherent and:

Close together

At a far off distance

Opposite to each other

Coinciding

66. Light appears to travel in straight lies since

It is reflected by the atmosphere

It is not absorbed by the atmosphere

Its velocity is very large

Its wavelength is very small

67. When the two surfaces of a thin film are parallel and the light is incident at a certain angle, _________ fringes are formed.

Straight

Circular

Parabolic

Elliptical

68. The locus of all points in the same phase of vibration is called:

Wave form

Wavelength

Wave front

Wave number

69. Which effect provides direct experimental evidence that light is a transverse, rather than a longitudinal, wave motion?

The intensity of light from a point source falls off inversely as the square of the distance from the source

Light can be diffracted

Two coherent light waves can be made to interfere

Light can be polarized

70. A polarizer is used to

Increase intensity of light

Produce polarized light

Produce unpolarised light

Reduced intensity of light

71. On a rainy day, if there is an oil drop on tar road, colored rings are seen around this drop. This is because of

Interference pattern produced due to thin oil film

Polarization

Diffraction pattern

Total internal reflection of light

72. The phenomenon of bending of light waves around the edges of an obstacle or a narrow opening is called.

Refraction

Reflection

Diffraction

Transmission

73. Choose the correct statement

Rays may be normal to wave front

Rays are not normal to wave front

There is no relationship between rays and wave fronts

Rays are normal to wave front

74. The idea of light as wave produced by

Michelson

Thomos young

Huygen

Newton

75. Signal from a remote control to the device operated by it tracels with the speed of:

Light

Supersonics

Sound

Ultrasonics

Page 4 of 4

76. Which effect provides direct experimental evidence that light is a transverse, rather than a longitudinal, wave motion?

Two coherent light waves can be made to interfere

The intensity of light from a point source falls off inversely as the square of the distance from the source

Light can be polarized

Light can be diffracted

77. Which of the following properties show light is transverse wave in nature?

Interference

Reflection

Polarization

Diffraction

78. Intensities of the two waves of light are l and 4l. The maximum intensity of the resultant wave after superposition is

25l

16l

79. In Huygen’s wave theory, the locus of all points in the same state of vibration is called

Vibrator

A ray

Wave front

A half-period zone

80. A thin film is a transparent medium whose thickness with the wavelength of light are

Not comparable

None of these

Comparable

Both

81. Which of the following is conserved when light waves interfere?

Momentum

Energy

Intensity

Amplitude

82. Can two head lights of car can produce interference

Partly produce interference

Yes

None of these

83. Diffraction fringes are

Distance between them increases

Distance between then decreases

They are adjacent with no space in between

Equally spaced

84. In Michelson interferometer to switch the fringe from bright to dark the mirror should be displaced through

?/2

?/3

?/4

?/6

85. In a plane polarized light

Vibration in all direction

Vibration in two mutually perpendicular directions

Vibration take place in a direction perpendicular to the direction of propagation of light

No vibration at all

86. The condition for the bright fringes formed due to constructive interference in a diffraction grating is:

md cos θ = λ

d sin θ = mλ

d sin θ = 2λm

d sin θ = m/2 λ

87. Polarization occurs only in ________ waves

Matter waves

Transverse

Longitudinal

Mechanical waves

88. The splitting of white light into several colors on passing through a glass prism is due to

Refraction

Reflection

Diffraction

Interference

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5 Comments

Trendsetter says:

September 5, 2021 at 2:27 pm

Idea of light as a wave was proposed by Huygen not young.

The best says:

June 30, 2020 at 5:40 pm

Light is a type of energy which produces sensation of vision.

Chaudry Adnan says:

August 24, 2017 at 5:13 pm

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Abuzar says:

April 26, 2017 at 11:07 am

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umair ahmed says:

March 21, 2017 at 1:26 am

if some is one is using this website so plz reply

Important Lights and Optics Question and Answer

Physics Lights and Optics Practice Test Online With Explanation

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